Field of the Invention
The present invention relates to an image processing technique of adjusting the texture of an image.
Description of the Related Art
Recently, image capturing apparatuses, such as a digital camera, which capture an object such as a person and record it as a moving image have been used on the digital cinema production site. On the digital cinema production site, color grading for adjusting the quality of a shot image to a desired texture is generally performed in addition to cut editing. The color grading processing is performed using a color grading apparatus in an editing studio or the like after shooting. However, in another type of workflow, rough color grading is performed upon shooting at the filming location and only fine color grading is performed after shooting. By performing rough color grading in advance, the load of color grading performed after shooting can be decreased.
When performing color grading, it takes time to perform all color grading processing manually from scratch and bring the image quality close to a desired texture. Especially in color grading at the filming location, the situation of an object may change every moment. It is therefore necessary to quickly perform color grading and adjust the image quality to a desired texture.
To achieve this, there is known a workflow in which color grading parameters for reproducing a desired texture are read to bring the image quality close to a target texture to a certain degree, and then final adjustment is performed manually. This color grading processing generally uses ASC-CDL parameters. The ASC-CDL (to be also referred to as a CDL (Color Decision List) hereinafter) has been generated and recommended by the ASC (American Society of Cinematographers) Technology Committee. At present, the ASC-CDL is used in many color grading processes. The CDL defines the methods of calculating the gain, gamma, and the like, as basic color grading processing. By generating in advance a CDL which reproduces a desired texture and performing color grading by using the CDL, the number of color grading processes can be greatly reduced.
For example, Japanese Patent Laid-Open No. 2003-189229 has disclosed a technique for obtaining an image of a desired texture by using image editing information like the above-mentioned CDL.
As described above, the number of color grading processes can be greatly reduced by generating in advance a CDL which brings the image quality close to a desired texture, and performing color grading by using the CDL. However, even if color grading is performed using the CDL generated in advance, a texture assumed from the CDL may not be obtained. For example, when color grading is performed to obtain an overall cold color texture in order to express a cold texture, the CDL values need to be changed depending on the color temperature of a light source which illuminates an object. This is because, even when color grading is performed to obtain the same cold color texture, the correction amount of color correction differs between a case in which a warm color scene having a low color temperature of the light source is changed into a desired cold color texture, and a case in which a cold color scene originally having a high color temperature of the light source is changed into a desired cold color texture. For this reason, the image quality cannot be brought close to a desired texture assumed from the CDL unless processing is performed using a CDL suited to an image to undergo color grading.